1. Field of the Invention
The present invention relates to an acetal group containing norbornene copolymer for use in a photoresist composition, a method for producing the same, and a photoresist composition containing the same. More particularly, the present invention relates to an acetal group containing norbornene copolymer that has improved properties and that includes norbornene or norbornene derivatives as its main chain. The invention also relates to an easy method for producing the copolymer.
2. Description of the Related Art
Lithography today has become a core technology in accomplishing large scale integrity of a memory semiconductor, DRAM. Specifically, improved lithography technology capable of forming finer patterns now is required in manufacturing VLSI (very large scale integrated circuit). In order to meet this requirement, it has become increasingly important to provide resist materials having high efficiency.
In general, photoresist compositions typically should exhibit transparency at an exposure wavelength, have excellent etching resistance, heat resistance and adhesion strength. In addition, photoresist compositions that are used in a lithography process with an excimer laser should be developable in a 2.38 weight % aqueous solution of tetramethyl ammonium hydroxide (TMAH). It is very difficult, however, to synthesize a photoresist resin that satisfies all of these requirements. For example, acrylic polymers have attracted attention for their ease of synthesis and low light-absorptivity at a light wavelength of 200 or less nm, but they have poor dry etching resistance.
In order to improve the etch resistance of these acrylic polymers, alicyclic unit""s have been introduced into the main chain or the side chain of acryl-based copolymers. Examples of alicyclic units introduced into the main chain of an acryl-based copolymer include norbornene, norbornene derivatives, cyclodiene and nortricyclene, and the like. Examples of alicyclic units introduced to the side chain of an acryl-based copolymer include isobornyl, menthyl, tricyclodecanyl, norbornyl, tetracyclododecyl, adamantyl and the like. Copolymers having alicyclic units introduced into its side chain usually have an acrylic polymer as its main chain, and the content of its alicyclic units typically is less than 50 weight % of the total copolymer. As a result, copolymers having alicyclic units in its side chain exhibit poor solubility in an alkaline aqueous solution, and exhibit poor adhesive strength to a substrate because alicyclic units introduced increase Tg (glass transition temperature) and hydrophobicity of the polymer. These copolymers also often suffer from problems due to fragility and poor sensitivity. On the other hand, copolymers having alicyclic units introduced into its main chain exhibit excellent dry-etching resistance and thermal properties and is advantageous because side chains having functionalities required for patterning can be introduced. Thus, many research has been conducted to obtain a matrix resin, of which the main chain is composed of an alicyclic structure.
In general, polymerization methods such as radical polymerization, cationic polymerization, addition polymerization, or ring-opening polymerization have been used to obtain the conventional multicyclic polymers such as norbornene polymers and norbornene derivative polymers. However, these methods are problematic in that the polymerization yield typically is low and their uses are restricted to monomers having polarity. Due to the complicated structures of most catalysts used for polarization, these methods may be affected by moisture during polymerization, and thus, only dry hydrocarbon solvents or dry halogenated aromatic solvents can be used.
The description herein of certain disadvantages associated with known photoresist compositions and polymers used therein is not intended to limit the present invention. Indeed, the present invention may include some or all of the polymers and photoresist compositions described above, without suffering from the same disadvantages.
In an effort to solve these problems, It is a feature of the present invention to provide norbornene-based copolymers that have excellent transparency, resolution, sensitivity and etching resistance and that are useful in lithography processes for making very large scale integrated semiconductor with an excimer laser. It is another feature of the present invention to provide a simple and easy preparation method of the photoresist norbornene-based copolymers of this invention. It is still another feature of the present invention to provide a photoresist composition useful in lithography processes for making very large scale integrated semiconductor with an excimer laser.
According to an aspect of the present invention, there is provided a novel acetal group containing norbornene copolymer useful in a photoresist composition, the copolymer being represented by the following Formula 1. 
wherein R1 is C1-12 linear, branched or cyclic alkyl group; R2, R3, R4 and R5 are independently hydrogen, fluorine, methyl or trifluoromethyl;
R6 and R7 are independently hydrogen or C1-10 linear or branched alkyl group, xe2x80x94(CH2)txe2x80x94R8, xe2x80x94(CH2)txe2x80x94OR8, xe2x80x94(CH2)txe2x80x94C(O)OR8, xe2x80x94(CH2)txe2x80x94C(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)OR8, or xe2x80x94(CH2)txe2x80x94C(O)OCH2OR8 in which, R8 is hydrogen, fluorine, C1-12 linear, branched, cyclic alkyl group or cyclic alkyl group containing ketone group, and t is an integer of 0 to 6, or R6 and R7 optionally may be attached to each other to form a ring; and
l, m and n are integers such that the ratio of l/(l+m+n) is from about 0.1 to about 0.99, the ratio of m/(l+m+n) is from about 0 to about 0.3 and the ratio of n/(l+m+n) is from about 0.01 to about 0.6; and
o, p, q, r and s each is independently an integer of from 0 to 2.
Another feature of an embodiment of the present invention relates to a method of preparing a photoresist norbornene-based copolymer, comprising:
addition polymerizing a monomer represented by the following Formula 2 and a monomer represented by the following Formula 3 in the presence of a palladium (II) catalyst in water or in an organic solvent comprising water; and
acetalyzing a portion of the acidic functional groups of the monomer represented by the Formula 2. 
wherein R2, R3, R4 and R5 are independently hydrogen, fluorine, methyl or trifluoromethyl;
R6 and R7 are independently hydrogen or C1-10 linear or branched alkyl group, xe2x80x94(CH2)txe2x80x94R8, xe2x80x94(CH2)txe2x80x94OR8, xe2x80x94(CH2)txe2x80x94C(O)OR8, xe2x80x94(CH2)txe2x80x94C(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)OR8, or xe2x80x94(CH2)txe2x80x94C(O)OCH2OR8, in which, R8 is hydrogen, fluorine, C1-12 linear, branched, cyclic alkyl group or cyclic alkyl group containing ketone group, and t is an integer of 0 to 6, or R6 and R7 optionally may be bonded with each other to form a ring; and
o, p, q, r and s each is independently an integer of 0 to 2.
Another feature of an embodiment of the present invention relates to a method of making a photoresist norbornene-based copolymer, comprising addition polymerizing a monomer represented by the following Formula 2, a monomer represented by the following Formula 3 and an acetal-substituted norbornene-based monomer represented by the Formula 4 in the presence of a palladium (II) catalyst in water or in an organic solvent comprising water. 
wherein R1 is C1-12 linear, branched or cyclic alkyl group; R2, R3, R4 and R5 are independently hydrogen, fluorine, methyl or trifluoromethyl;
R6 and R7 are independently hydrogen atom or C1-10 linear, branched alkyl group, xe2x80x94(CH2)txe2x80x94R8, xe2x80x94(CH2)txe2x80x94OR8, xe2x80x94(CH2)txe2x80x94(O)OR8, xe2x80x94(CH2)txe2x80x94(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)R8, xe2x80x94(CH2)txe2x80x94OC(O)OR8, or xe2x80x94(CH2)txe2x80x94C(O)OCH2OR8, in which, R8 is hydrogen atom, fluorine atom, C1-12 linear, branched, cyclic alkyl group or cyclic alkyl group containing ketone group, and t is an integer of 0 to 6, or R6 and R7 optionally may be bonded with each other to form a ring; and
o, p, q, r and s each is independently an integer of 0 to 2.
An additional feature of an embodiment of the present invention relates to a photoresist composition comprising (a) the norbornene-based copolymer of this invention, (b) a photo acid generator, and (c) an organic solvent.
Other features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.